Inertia is a fundamental property of mass, indicating that an object will maintain its state of motion unless acted upon by an unbalanced force. It is not a quantifiable measure but is related to an object's mass and shape, with greater mass resulting in greater inertia. This concept is often confused with momentum, which is the product of mass and velocity, leading to misconceptions about inertia. While inertia describes an object's resistance to changes in motion, momentum explains the difficulty of stopping or altering the path of a moving object. Understanding these distinctions is essential for grasping the principles of classical physics.